This application is being submitted to PA-18-591 in accordance with NOT-OD-18-194. Persons with Down syndrome (DS) develop Alzheimer?s disease neuropathology, with relative certainty, as they age. A consortium of investigators dedicated to the focused study of DS has already been established, i.e., the ABC-DS. Because the Alzheimer?s Disease Centers (ADC) with appropriate expertise may want to enroll a cohort of DS persons, this supplement will make possible a comparable means of data collection. Then, ADC data could be harmonized nationally and analyzed in combination with the more concentrated data collected by ABC-DS, thus advancing knowledge in the field. The ADCs have in place a standardized clinical examination and data collection protocol (the Uniform Data Set, UDS) for all Clinical Core enrollees. Version 3 of the UDS was implemented in 2015. Unfortunately, there are aspects of DS, which would make it difficult to apply the complete UDS to DS subjects in order to adequately evaluate the occurrence of cognitive change specific to, or progressing toward dementia, as well as determining whether these cognitive symptoms may correlate with pathologic changes related to Alzheimer?s disease (e.g., in vivo biomarkers). Thus, there is a need to develop a ?DS Module? to the UDS, consistent with ABC-DS experience, which can be applied at ADCs for the evaluation of DS persons whom they would enroll.